High-palladium alloys have become popular for metal-ceramic restorations and implant-supported prostheses, because of their much lower cost than gold alloys and their good mechanical properties. However, there is limited scientific knowledge about relationships between complex structures of these alloys and relevant clinical properties. For example, small compositional differences can result in unexplained substantial changes in mechanical properties, as well as metal-ceramic bond strength. A three-year project is proposed to continue research on structure-property relationships for commercial high-palladium alloys. Transmission electron microscopy (TEM) will be used to complete analyses of the tweed ultrastructure and learn whether this constituent dominates all high-palladium alloys, to determine the fundamental mechanisms for hardness and strength of these alloys, and to obtain basic information about creep and distortion of castings during fabrication of dental prostheses. Scanning electron microscopy (SEM) with x-ray energy-dispersive elemental analyses (EDS), x-ray photoelectron spectroscopy (XPS) and TEM will provide fundamental knowledge about the differences in metal-ceramic bond strength for various alloys. SEM/EDS analyses will also provide new information about the major roles of secondary microstructural phases for the hardness of these alloys, a matter of clinical concern. Flexural and tensile creep experiments will be performed at stress and high-temperature regimes appropriate for the fabrication of dental prostheses, to compare the creep resistance of representative alloys and determine whether single or multiple creep mechanisms are involved. Cyclic loading experiments using appropriate in vitro media, and both unnotched and notched test specimens, will establish the roles of alloy composition and microstructure for fatigue limits and crack propagation rates. XPS analyses of fracture surfaces will provide information about roles of various phases and impurities for failure. The results from this project will guide scientific development of new high-palladium alloys with optimum structures and properties, permitting delivery of improved, less expensive dental care to the public.